Patient-reported outcome (PROs) instruments complement conventional clinical outcomes by examining from the perspective of patients how they feel, what they perceive they can do, which types of activities they believe they can participate in, and how satisfied they are with their health and lives. To advance the science of PRO assessment, the NIH launched in 2004 the Patient Reported Outcome Measurement Information System (PROMIS(r)). Although a key objective of PROMIS is to provide PROs for research and clinical practice across the life course, there is remarkably little known about the validity of PROMIS for children with chronic diseases or the degree to which PROMIS detects clinically meaningful changes in children's health. To address these scientific needs, we propose to create the Child-Centered Outcomes in Practice and Research (COPR) Center of Excellence, which will be devoted to rigorously examining and documenting PROMIS' clinical validity for children with chronic conditions. COPR comprises three research projects focusing on pediatric Crohn's disease, chronic kidney disease, and cancer. The projects are linked by common measures of children's Experienced Well-Being (a concept that subsumes both suffering and happiness), clinical validation methods, and infrastructure. Each project will assess the content validity, clinical meaningfulness of scores, responsiveness to clinical change, and longitudinal construct validity of the PROMIS Pediatric pain interference, fatigue, psychological stress experiences, and positive affect measures. The COPR approach will increase the measures' psychometric and clinical maturation according to PROMIS standards and provide evidence required by the FDA to qualify PRO instruments for clinical trials. The COPR team integrates: a PROMIS research group that developed 10 of the 20 extant PROMIS pediatric measures and helped lead the PROMIS initiative over the past 6 years; a PCORI-funded clinical data research network (PEDSnet) with deep expertise in electronic health record and PRO data management, quality assessment and reporting; a national network of pediatric gastroenterologists embarking on a PCORI-funded clinical trial for children with Crohn's disease; a national network of pediatric nephrologists who are conducting an NIH-funded cohort study on children with chronic kidney disease; and, one of the nation's largest pediatric oncology clinical centers located at St. Jude Children's Research Hospital. The COPR infrastructure will: facilitate coordination across its three research projects; standardize clinicl validation methods and informatics resources; synthesize results across the three projects; develop standards-based instrument dossiers to enhance clinical adoption of PROMIS and facilitate FDA qualification of PROMIS measures as clinical trial end-points; and, support collaboration with other PEPR research programs. COPR is optimized to successfully accomplish its three research projects, and its infrastructure can be readily scaled to support the informatics, statistical, and administrative needs of multiple other PEPR research initiatives.